One night, we see a giant laser from outer space burn a message into the Moon (in some human language or another):

Earth Creatures, you are hereby evicted from Earth. Take your belongings and leave in X days. You no longer own on any land on Earth. If you try to prevent us from repossessing it, you will be exterminated.

My question is, what should X be, so that humans have time to evacuate the Earth?

The aliens clearly have the capability to make good on their words.

All humanity is united in this effort.

We will never be able to return to Earth, so we must take everything we need into space.

The message also specifies that we may not be in any sort of orbit around the Earth. This includes going to the moon.

What is the smallest X that would allow a small band of humans to escape and start the human race over again? The majority of humans to escape?

$\begingroup$All the demolition orders have to be on display for 50 years in the local planning department on Alpha Centauri.$\endgroup$
– hisAug 3 '15 at 21:18

2

$\begingroup$If you see people as a resource (workers) like capitalism does, you can easily calculate that the value of 99% of humans is less than the cost of taking them to space. There could well be a scam where the rich pretend that they intend to take everyone to space to keep people happy though...$\endgroup$
– VarrickAug 3 '15 at 21:31

1

$\begingroup$IF we tried to evacuate 16 million people a day we would still not be able to evacuate everyone in a year - just saying for reference.$\endgroup$
– MikeyAug 3 '15 at 21:41

2

$\begingroup$@PyRulez "one family" is infinitely different from "a whole planet". Try to find an example of any civilization that was evicted in this silly way and just accepted it, instead of fighting.$\endgroup$
– o0'.Aug 3 '15 at 22:36

2 Answers
2

Your precondition that “All humanity is united in this effort” is a bit ambiguous and leaves open lots of interpretations, some that are severely unrealistic and others that are pretty dire. If the entire world were suddenly made aware of a concrete ticking clock on their lives, society would very likely collapse in short order.

Considering a Technical Estimate

In the extremely unrealistic scenario that the entire human population is willing to throw its combined daily might behind saving the species, we would need to reach the minimum viable population for the human species. Technical estimates seem to vary on this widely, but sources seem to indicate somewhere between 100-200 people, with massive social engineering, might be enough to repopulate. I think it’s pretty important to note here: there would be absolutely nothing fun about being in this group of people. Some might jump to say that the wealthy would all blast off leaving us behind, but the quality of life of these people is going to be devastatingly different for generations. People with strong skills and favorable genetic backgrounds will be required, and women are likely to have an extremely unpleasant time, since their overwhelming priority will be to safely give birth to children from a variety of different genetic backgrounds for as long as they can. This isn’t a picnic, and your duties aren’t going to be optional.

Launching 200 people to Mars with an unlimited budget and human participation would neither be particularly challenging nor all that realistic, which is why I don’t want to focus my estimates on the technical aspect. Instead, I want to look at things at a more social level.

Smallest X: 60 years

As mentioned earlier, when the entire human species becomes convinced that their extermination is imminent, there will be absolute chaos. Even the best intentioned people will have an extremely difficult time creating a minimum viable population on Mars or elsewhere if society has collapsed. Therefore, the best chance for a small X is to place the end date after the influential portion of the population (ages 16 and up) are likely to be dead. Parents will be terrified for their children and the birthrate will plummet. But the people who need to keep doing their jobs no longer have an imminent threat to their lives that will destroy social structure. Sixty years seems like a fairly stable timeframe for this situation. For today’s youth in first world countries, 80 years would be seen as a decent, if not good, life. With such a time limit imposed, it is not only feasible to set up a strong and redundant system of MVP colonies, but you could actually rely on today’s social fabric to help you do it.

Largest X: Thousands of years

This estimation is much more nebulous, because if you’re talking about smoothly transitioning the entire species off of Earth it’s going to be a much different ballgame. Moving that many people into space really isn’t feasible with current resources and technology, so the more time you can provide for technological progress, the better. It’s also interesting to consider whether or not anyone would care if such a large time limit was imposed. This would likely alarm scientists, but in many ways a limit on a scale of millennia is comparable to the threat of climate change or even the eventual death of our sun. If it’s too far off or too gradual, it simply doesn’t impact a human life on the order of decades. If the aliens are really that technologically advanced and care that much about the human species, they should be offering their help to relocate us like responsible stellar neighbors.

The answer

The only answer those silly aliens would get would be "lol, screw you, are you insane?". Seriously, there is absolutely zero chance a whole civilization would just comply with such an unreasonable request, instead of fighting. Fighting is actually much simpler and even has better odds of success.

As a proof, try to find any example in our history where this happened to a large scale ("one family" definitely does not count, and even "one village" is far from being even remotely comparable).

How would they do it, and why

But even trying to ignore this, they would never make such a silly request, unless they were completely insane. Now, if they are completely insane then there's absolutely no point on discussing this, since the answer would be "whatever". So let's assume they are not out of their minds.

If their goal is to evict humans, then they perfectly know that humans aren't capable, nor willing, of organising such a mass exodus.

If "killing them all" is an option, they would do just that, no fake ultimatum required.

Again, if you assume that there's a "space law" forcing them to give an ultimatum, then that law must also be immune to such a silly "trick", or that law is insane, and we are back to square 1. So we'll assume that they either genuinely do not want to kill us, or that if there's a law, it's not idiotic.

So, they want to evict us, they do not want to kill us, and they know we can't and won't do it ourselves… they would do it. They will provide transportation, destination, and stuff. Maybe they will lie to some people, claiming they would bring us to a nice place when it actually isn't, maybe not… still, the only sensible conclusion to such a dilemma is: they take care of the matter personally.

Finally

Also notice that doing it themselves would be much faster than waiting for us to do it. So they have an "occupied" planet, they want it, and they prefer to wait for 100 years for the occupants to calmly go away, instead of just "helping" them and be done in a few months or years? Again, this makes zero sense.

$\begingroup$Space Law says that if beings have infested your planet intelligent enough to do limited space exploration, you must give them a chance to move before exterminating them. I know this because I'm a space lawyer.$\endgroup$
– PyRulezAug 3 '15 at 23:04

$\begingroup$"Again, if you assume that there's a "space law" forcing them to give an ultimatum, then that law must also be immune to such a silly "trick", or that law is insane, and we are back to square 1. So we'll assume that they either genuinely do not want to kill us, or that if there's a law, it's not idiotic." Such a law would be idiotic, hence it's pointless to discuss it.$\endgroup$
– o0'.Aug 3 '15 at 23:05

2

$\begingroup$So, they want to evict us, they do not want to kill us, and they know we can't and won't do it ourselves… they would do it. They will provide transportation, destination, and stuff. Maybe they will lie to some people, claiming they would bring us to a nice place when it actually isn't, maybe not… still, the only sensible conclusion to such a dilemma is: they take care of the matter personally.$\endgroup$
– o0'.Aug 3 '15 at 23:12

1

$\begingroup$-1 for rejecting the premise of the question.$\endgroup$
– MarkAug 4 '15 at 1:41

4

$\begingroup$@Mark are you serious? "the question is wrong" is a perfectly fine answer, all-around the SE network. Especially if… the question is wrong.$\endgroup$
– o0'.Aug 4 '15 at 7:05